The study is an intraindividual comparison of two methods. The number of subjects to be enrolled is 47. Patients will receive both treatments in a single visit: A first period of 2.5 hours of illumination with Phos-Istos device followed by a continuous red light spectrum (between 7 and 10 minutes) with Aktilite® after an appropriate incubation of MAL (methyl aminolevulinate). Patients will complete a pain assessment scale after receiving both treatments. 3 follow-up visits will be then scheduled